The role of adenosine in adrenal secretion has been investigated. Adenosine containing compounds that can be converted by a number of enzymes on the external surface of the Y-1 adrenal tumor cell membrane all stimulate steroidogenesis maximally probably through a receptor on the cell surface. The effect is inhibited by adenosine deaminase and theophylline. Adenosine also stimulates adenylate cyclase in membranes prepared from Y-1 cells but in this system it acts as only a partial agonist. BIBLIOGRAPHIC REFERENCES: Wolff, J. and Cook, G.H.: Activation of steroidogenesis and adenylate cyclase by adenosine in adrenal and Leydig tumor cells. J. Biol. Chem. 252: 687-693, 1977.